Direct time‐resolved measurements of the linear and nonlinear electronic impulse response of a high‐speed gallium arsenide metal semiconductor field‐effect transistor have been made by using picosecond optical pulses to drive high‐speed photoconducting electronic pulse generators and sampling gates. High resolution, jitter‐free measurements with excellent signal‐to‐noise showed the field‐effect transistor to have a fast full width at half‐maximum response of approximately 25 ps, and a slower fall time of 75 ps.